'\" et
.TH SETSOCKOPT "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
setsockopt
\(em set the socket options
.SH SYNOPSIS
.LP
.nf
#include <sys/socket.h>
.P
int setsockopt(int \fIsocket\fP, int \fIlevel\fP, int \fIoption_name\fP,
    const void *\fIoption_value\fP, socklen_t \fIoption_len\fP);
.fi
.SH DESCRIPTION
The
\fIsetsockopt\fR()
function shall set the option specified by the
.IR option_name
argument, at the protocol level specified by the
.IR level
argument, to the value pointed to by the
.IR option_value
argument for the socket associated with the file descriptor specified
by the
.IR socket
argument.
.P
The
.IR level
argument specifies the protocol level at which the option resides. To
set options at the socket level, specify the
.IR level
argument as SOL_SOCKET. To set options at other levels, supply the
appropriate
.IR level
identifier for the protocol controlling the option. For example, to
indicate that an option is interpreted by the TCP (Transport Control
Protocol), set
.IR level
to IPPROTO_TCP as defined in the
.IR <netinet/in.h> 
header.
.P
The
.IR option_name
argument specifies a single option to set. It can be one of the
socket-level options defined in
.IR "\fB<sys_socket.h>\fP"
and described in
.IR "Section 2.10.16" ", " "Use of Options".
If
.IR option_name
is equal to SO_RCVTIMEO or SO_SNDTIMEO and the implementation supports
setting the option, it is unspecified whether the
.BR "struct timeval"
pointed to by
.IR option_value
is stored as provided by this function or is rounded up to align with
the resolution of the clock being used. If
\fIsetsockopt\fR()
is called with
.IR option_name
equal to SO_ACCEPTCONN, SO_ERROR, or SO_TYPE, the behavior is unspecified.
.SH "RETURN VALUE"
Upon successful completion,
\fIsetsockopt\fR()
shall return 0. Otherwise, \-1 shall be returned and
.IR errno
set to indicate the error.
.SH ERRORS
The
\fIsetsockopt\fR()
function shall fail if:
.TP
.BR EBADF
The
.IR socket
argument is not a valid file descriptor.
.TP
.BR EDOM
The send and receive timeout values are too big to fit into the timeout
fields in the socket structure.
.TP
.BR EINVAL
The specified option is invalid at the specified socket level or the
socket has been shut down.
.TP
.BR EISCONN
The socket is already connected, and a specified option cannot be set
while the socket is connected.
.TP
.BR ENOPROTOOPT
.br
The option is not supported by the protocol.
.TP
.BR ENOTSOCK
The
.IR socket
argument does not refer to a socket.
.P
The
\fIsetsockopt\fR()
function may fail if:
.TP
.BR ENOMEM
There was insufficient memory available for the operation to complete.
.TP
.BR ENOBUFS
Insufficient resources are available in the system to complete the
call.
.LP
.IR "The following sections are informative."
.SH "EXAMPLES"
None.
.SH "APPLICATION USAGE"
The
\fIsetsockopt\fR()
function provides an application program with the means to control
socket behavior. An application program can use
\fIsetsockopt\fR()
to allocate buffer space, control timeouts, or permit socket data
broadcasts. The
.IR <sys/socket.h> 
header defines the socket-level options available to
\fIsetsockopt\fR().
.P
Options may exist at multiple protocol levels. The SO_ options are
always present at the uppermost socket level.
.SH "RATIONALE"
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Section 2.10" ", " "Sockets",
.IR "\fIbind\fR\^(\|)",
.IR "\fIendprotoent\fR\^(\|)",
.IR "\fIgetsockopt\fR\^(\|)",
.IR "\fIsocket\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<netinet_in.h>\fP",
.IR "\fB<sys_socket.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
